1. Filed of the Invention
This invention relates to a magnetic head and more particularly to a composite magnetic head consisting of a plurality of head assemblies which is capable of reducing cross-feed between a writing head and a reading head.
2. Description of the Prior Art
Recently, an apparatus referred to in general as a streamer has been employed for preventing erroneous erasure of data recorded in a hard disc drive unit of a computer. A single-reel tape cartridge disclosed in U.S. Pat. No. 4,452,406, which is manufactured and sold by IMB as so-called "3480 cartridge", is now known as a preferable one to be used in the streamer. A specific format for the streamers utilizing the 3480 cartridge has been proposed by a HI/TC (Half Inch Tape Cartridge) group. According to this format, high-density recording and/or reproducing of 24 tracks can be made on a half-inch magnetic tape in the 3480 cartridge. The magnetic tape is running in both directions at high speed, while being in contact with a magnetic head of a write/read/write, 2-channel, 6-gap type.
A suitable construction for the magnetic head in accordance with the format has also been proposed in, for example, Japanese patent provisional publications Nos. (Hei) 1-179204, 1-179206 through 1-179209, 1-179211 and 1-179212. The magnetic head disclosed in these publications will be described in reference to FIG. 5. A pair of 2-channel writing head assemblies 3 and 16, and a 2-channel reading head assembly 10 are secured on an aluminum base block 22. The first writing head assembly 3 is made operative with respect to the magnetic tape running in the forward direction and comprises a pair of ring cores 2.sub.1 and 2.sub.2 which are interposed between sliders 1.sub.1 and 1.sub.2 and sliders 1.sub.2 and 1.sub.3, via glass material spacers (not shown) of 50.about.70.mu., respectively. Gaps in the order of 1.8.mu. are formed in the respective ring cores 2.sub.1 and 2.sub.2. Coils (not shown) are provided only on the left sides of the ring cores 2.sub.1 and 2.sub.2, respectively. A guard block 5 having coil receiving recesses 4.sub.1 and 4.sub.2 is arranged on the left side of the first writing head assembly 3, whereas a shield block 7 having coil receiving recesses 6.sub.1 and 6.sub.2 on the right side thereof. The second writing head assembly 16 is made operative with respect to the magnetic tape running in the reverse direction. A pair of ring cores 16.sub.1 and 16.sub.2 having gaps in the order of 1.8.mu. are interposed between sliders 15.sub.1 and 15.sub.2 and sliders 15.sub.2 and 15.sub.3, via glass material spacers (not shown) of about 50.about.70.mu., respectively. The ring cores 16.sub.1 and 16.sub.2 are provided with coils (not shown) respectively on the right sides thereof. A shield block 18 having coil receiving recesses 17.sub.1 and 17.sub.2 is mounted on the left side of the second writing head assembly 16, and a guard block 20 having coil receiving recesses 19.sub.1 and 19.sub.2 on the right side thereof. The reading head assembly 10 for the magnetic tape running in the forward/reverse directions includes a pair of ring cores 9.sub.1 and 9.sub.2 interposed between sliders 8.sub.1 and 8.sub.2 and sliders 8.sub.2 and 8.sub.3, via glass material spacers (not shown) of about 50.about.70.mu., respectively. Gaps in the order of 0.7.mu. is formed in the respective ring cores 9.sub.1 and 9.sub.2. The ring cores 9.sub.1 and 9.sub.2 are provided on opposite sides thereof with coils (not shown), respectively, which are received in recesses 11.sub.1 and 11.sub.2 of a shield block 12 arranged on the left side of the assembly 10 and in recessed 13.sub. 1 and 13.sub.2 of another shield block 14 arranged on the right side thereof. The composite magnetic head thus constructed is adapted to be in contact with the magnetic tape at specific portions 21.sub.1 through 21.sub.5 which are mirror-finished to guarantee smooth running of the magnetic tape. The respective ring cores, sliders, shield blocks and guard blocks are all made from ferrite. Between the shield blocks 7 and 12 and the shield blocks 14 and 18, there will leave gaps in a predetermined distance of about 1 mm.
With the magnetic head described above, magnetic flux which might leak out of the head assemblies 3, 10 and 16 will substantially be absorbed into the shield blocks and/or guard blocks arranged in the opposited sides thereof. There are provided gaps between the shield blocks 7 and 12; and 14 and 18, respectively. Moreover, the ring cores 2.sub.1 and 2.sub.2 ; and 16.sub.1 and 16.sub.2 of the writing head assemblies 3 and 16 are provided with the coils on the respective one side which is located far from the coils of the reading head assembly 10. By these reasons, even if the magnetic flux should leak out of the coil positions of the head assemblies, there will be substantially no risk of arising cross-feed between the heads.
In some cases a composite magnetic head of another type in which a first reading head, a single writing head and a second reading head are arranged in this order is preferred. Suppose that the above-described magnetic head of write/read/write arrangement is modified into such a read/write/read magnetic head. However, since the ring cores of the reading head should preferably be provided with the coils on the opposite sides thereof for the purpose of improving a S/N ratio, there may be a tendency to arise cross-feed between the writing head and one of the reading heads located in vicinity to the coiled side of the writing head. Accordingly, the above-described construction is not suitable to the read/write/read magnetic head.
Various counterplans against the cross-feed problem have been proposed. For example, in Japanese patent publication No. (Sho) 50-31817, a shield block having high permeability is arranged between a writing head and a reading head and an auxiliary coil is wound around the shield block for generating a magnetic flux to cancel the cross-feed from the writing head. Provision of the auxiliary coil is troublesome and will therefore increase the manufacturing costs. Moreover, this counterplan is very difficult to be applied to a composite magnetic head because a substantial space for the auxiliary coil would not be available therein.
In Japanese patent publication No. (Sho) 50-5925, as well as in the above-recited publication No. (Sho) 50-31817, it has been tought that high frequency components of the cross-feed signal may be removed by shield plates attached to the front faces of the magnetic head, excluding the gaps. The shield plates are made of non-magnetic, conductive material such as gold, silver and copper. However, in order to cope with the cross-feed problem, it is necessary that the entire faces excluding the gaps should be covered with the shield plates, which could not be expected in the case of a composite magnetic head having complicated shape in the front faces.